Isotope splitting of theCl−gap mode in KI

Abstract

High-resolution measurements of the far-infrared lattice gap mode of ${\mathrm{Cl}}^{-}$ in KI at 1.2 °K reveal the presence of three absorption lines at 76.46 ± 0.05, 76.75 ± 0.02, and 77.08 ± 0.02 ${\mathrm{cm}}^{-1\mathrm{}}$. These lines are explained in a model which includes the isotope splitting resulting from both the ${\mathrm{Cl}}^{-}$ impurity and its ${\mathrm{K}}^{+}$ nearest neighbors. In addition, the full linewidth of the ${77.08-\mathrm{c}\mathrm{m}}^{-1\mathrm{}}$ line is determined to be 0.06 ± 0.02 ${\mathrm{cm}}^{-1\mathrm{}}$ and is ascribed to strain broadening.